WordPress is a rich ecosystem and its plugins & themes can do anything and everything. This is a huge advantage for users but also a challenge for VersionPress as some of these external pieces of code might need special handling.

This page provides general overview and there are three sub-pages discussing specific:

There are two main groups of external plugins & themes from VersionPress' point of view:

Those that work out of the box

Those that require specific support

Though we don't have concrete stats, many plugins and almost all themes fall into the first category, which is good. It's mostly if the plugin / theme is relatively simple or does things "the WordPress way", i.e., uses the built-in database tables, standard functions etc.

However, there are also plugins that are either not quite well coded or so complex that they require specific support. To a lesser extent, this is also true for themes, mostly the "page builder" themes that possibly use their own database tables, etc. But it is far more common for plugins.